Chemical and Rheological Properties of Viscous Polysaccharides from Three Species of Yam (Dioscorea)

Abstract

Viscous Polysaccharides were extracted from three species of Yam, Jinenjo (Dioscorea japonica THUNB.), Tsukune-imo (D. opposita THUNB.), and KaU-09 (D. alata L.) which was introduced from South-East Asian district. These yam viscous polysaccharides (Y.V.P.) were finally purified through ion-exchange resins ater treatment with SDS-EtOH five times to remove proteinic and phosphorous impurities. Chemical and rheological properties of Y.V.P. were comparatively estimated and the following results were obtained. (1) Carbohydrate contents in the acid-hydrolysates were analysed to be 53-55%, and 90% of the resulting reducing sugars was mannose. The rest of sugars consisted of small amounts of arabinose, glucose and galactose, and a trace of xylose and rhamnose was also detected. Acetyl group was found to be about 2 moles per one sugar residue. There were little or no difference in sugar components among these three species of yam. (2) Protein contents of these Y.V.P. ranged from 2.0% to 2.2% and their amino acid compositions were almost similar to each other. The major amino acids were Asp., Glu., Ala., Ser. and Gly. (3) Viscosity of the Y.V.P. solutions which were treated with SDS and EtOH was almost similar to each other. Viscosity of the Y.V.P. solution increased remarkably after treatment through ion-exchange resins, and the increase was largest for KaU-09. Viscosity of finally purified Y.V.P. solution from KaU-09 was highest in water but lowest in 0.1M NaCl. Change of reduced viscosity against concentration in the purified Y.V.P. solution was larger in case of Jinenjo and Tsukune-imo than KaU-09, suggesting that interaction between Y.V.P. molecules was more strong in Jinenjo and Tsukune-imo than in KaU-09. These results show that rheological behavior of finally purified Y.V.P. from three species of yam was not equal.